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posture
posture biomechanics
76
Anatomy
Graduate
12/10/2011

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Term
what is BOS
Definition
base of support = contact with ground
Term
what is COG
Definition
center of gravity = mass at one point where line of gravity pulls straight down
Term
what is COP
Definition
center of pressure = line where COG meets the ground
Term
what produces external moments
Definition
external forces: gravity, inertia, ground reaction force
Term
what produces internal moments
Definition
internal forces: muscles, ligaments, joint contact forces
Term
what information do we get from muscle spindles
Definition
instantaneous muscle length AND rate of change of muscle length
Term
what information do we get from golgi tendon organs
Definition
tension and rate of change of tension in tendon
Term
where are extrafusal muscle fibers
Definition
outside muscle spindle
Term
what innervates extrafusal muscle fibers
Definition
alpha motor neuron
Term
where are intrafusal muscle fibers
Definition
inside muscle spindle
Term
what innervates intrafusal muscle fibers
Definition
gamma motor neurons
Term
what are the names of the 2 types of sensory endings that come out of the muscle spindle
Definition
primary, secondary
Term
what is anothter name for primary?
Definition
Group 1a = dynamic
Term
what is another name for secondary
Definition
Group 2 = static
Term
what do primary/group 1a sensory signals tell us?
Definition
how the length of the muscle is changing
Term
what do group 2 sensory signals tell us?
Definition
instantaneous length of muscle
Term
where do group 1a and 2 sensory signals go?
Definition
spinal cord
Term
what does gamma motor neuron do?
Definition
tell intrafusal fibers when to contract and relax
Term
when the muscle is stretched, how does the firing of impulses change?
Definition
increases
Term
when the muscle is unstretched, how does the firing of impulses change?
Definition
decreases
Term
what is the input into a muscle spindle?
Definition
gamma motor neurons
Term
what are the outputs of the muscles spindle?
Definition
group 1a dynamic and group 2 static fibers (axons that go to spinal cord)
Term
example of monosynaptic stretch reflex
Definition
hammer on quads tendon causes quick stretch to muscle
Term
what happens in a monosynaptic stretch reflex?
Definition
1a primary fiber respons by sending signal up to spinal cord where it synapses on alpha motor neuron. Alpha motor neuron returns to extrafusal muscle fibers and makes them contract
Term
how many efferent fibers are gamma motor fibers?
Definition
one third
Term
what happens when a Ia response goes to spinal cord?
Definition
it will tell alpha neuron to contract muscle
Term
how do gamma efferents modify sensitivity of spindle?
Definition
contraction of gammas increaes sensitivity to stretch; relaxation of gamas decreases sensitivity to stretch
Term
what is the afferent signal that comes from golgi tendon organ?
Definition
group Ib fibers
Term
what do group 1b fibers tell us
Definition
static AND dynamic tension in tendon
Term
what is the function of the golgi tendon organ
Definition
inhibit the muscle that is contracting.
Term
where are golgi tendon organs
Definition
located in series with 10-15 muscle fibers at the myotendonous junction
Term
does the golgi tendon organ have a dynamic or static response?
Definition
both
Term
benefit of being bipedal
Definition
free to use upper extremities for other tasks
Term
disadvantages of being bipedal
Definition
increased stress on vertebra/pelvis/lower extremeties; reduced stability from reduced BOS
Term
goals of postural control
Definition
control the body's orientation In space, maintain COM within BOS, stabilize head with respect to vertical, do these things with minimal energy expenditure
Term
where is LOG at ankle in standing
Definition
anterior
Term
external moment at ankle
Definition
dorsiflexoin
Term
internal moment at ankle
Definition
plantarflexion
Term
where is LOG at head in standing posture
Definition
anterior
Term
what muscles produce internal moment to overcome external moment of gravity at head
Definition
cervical extensors
Term
where is LOG at hip in standing
Definition
slightly posterior
Term
external moment at hip
Definition
extension
Term
internal moment at hip
Definition
flexion
Term
what produces internal moment at hip
Definition
iliopsoas, ligaments
Term
where is LOG at knee in standing
Definition
slightly anterior
Term
what is the external moment at the knee
Definition
extension
Term
what is the internal moment at the knee
Definition
flexoin
Term
what provides internal moment at knee
Definition
passive support from posterior capsule
Term
what provides internal moment at ankle
Definition
plantarflexion from soleus
Term
what can someone with paraplegia do to stand?
Definition
if someone can't produce an active internal flexion moment, they can use the external extension moment from the posterior LOG along with passive internal "flexion" from iliofemoral ligament
Term
describe forward head posture
Definition
large external flexion moment causes large internal extension moment. Cervical extensors are overworked and lengthened.
Term
how does spine change in anterior pelvic tilt
Definition
anterior pelvic tilt causes increased lumbar lordosis and increased thoracic kyphosis
Term
what is swayback posture
Definition
lumbar lordosis, thoracic kyphosis
Term
where is LOG in swayback posture
Definition
farther posterior to hip joint
Term
where are ligaments stressed in swayback posture
Definition
anterior hip to prevent external flexion moment
Term
why do hip extensors become weak in swayback posture?
Definition
reliance on anterior hip ligaments leads to disuse atrophy of hip extensor muscles
Term
where is LOG of knee in flexed knee posture?
Definition
posterior
Term
what is the external moment at the knee in flexed knee posture
Definition
flexion
Term
what is the internal moment at the knee in flexed knee posture?
Definition
extension
Term
what provides interal extension moment at knee in flexed knee posture?
Definition
quads
Term
how does flexed knee affect other LE jionts?
Definition
flexed knee causes hip to flex and dorsiflexes ankle. This causes shortening of hip flexors => flexed hip posture
Term
what causes genu recurvatum?
Definition
quads weakness, diminished dorsiflexoin
Term
where is the LOG in normal knee standing posture?
Definition
anterior
Term
what opposes external extension moment at knee?
Definition
posterior capsule
Term
what is the result of genu recurvatum on the posterior capsule of the knee?
Definition
gets worse as it continues to stretch posterior capsule
Term
If I am standing and I pick up my left foot, what happens to my LOG?
Definition
shifts to Right
Term
If I am standing and I pick up my left foot, what happens to my center of pressure?
Definition
moves completely under right foot
Term
what is pes planus
Definition
low arch, flat foot, pronated
Term
what is pes cavus
Definition
high arch, supinated
Term
in relaxed sitting, where is LOG?
Definition
anterior
Term
in slumped sitting, where is LOG
Definition
further anterior
Term
what tissues support us during slumped sitting
Definition
passive tissues for support; ligaments hold you up against external flexion
Term
is pelvic tilted anteriorly or posteirorly in standing?
Definition
anteriorly
Term
how is lumbar lordosis affected in standing?
Definition
increases
Term
is pelvic tilted anteriorly or posteriorly in sitting?
Definition
posteriorly
Term
how is lumbar spine affected by sitting
Definition
flattens; decreased lumbar lordosis with posterior pelvic tilt
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